Many interactive computer systems available today utilize an input device held or otherwise manipulated by the user(s) to interact with the characters and/or landscape of a computer program, e.g. a game. For example, a conventional video game allows a user to hold a “gun” and “shoot” at clay pigeons on a display screen. The gun is connected with the game controller, either by a cord or by wireless link. The x-y position of the gun at the time the trigger is pulled is assessed by flashing an electronic marker across the screen. The image of the electronic marker is captured by a sensor on the input device, and the appearance of the captured image is used to assess the x-y position of the gun at the time the trigger was pulled. In this fashion, conventional interactive systems permit two-dimensional tracking of a user input device.
Two-dimensional tracking provides for limited interaction for the user with elements of a computer program, e.g. a game. For example, the previously mentioned game where a user can take aim and shoot at clay pigeons as they travel across a display screen. However, conventional systems do not track the movement of an input device as a user moves forward or backward in relation to a display screen. In conventional systems, the distance of the user from the display screen does not factor in to the interactive nature of the game.
Typically, the sensor is a photodiode. In conventional systems, the flashing of the electronic marker briefly interrupts the program (e.g. the game) and is typically detectable by the user. This interruption may be an annoying distraction to the enjoyment of the program or game. For example, in some systems, the whole screen may flash white for a time period that is detectable by the user.